Cold plate for dual refrigeration system

ABSTRACT

A cold plate includes two flow-wise isolated coolant (or refrigerant) passages (or sets of passages) for use in conjunction with separate refrigeration systems. The cold plate passages do not permit flow communication between distinct coolant (or refrigerant) paths. This permits two distinct cooling systems to operate in a redundant manner. Nonetheless, flow isolation is achieved while still maintaining tight thermal coupling between each path and the object, such as an electronic computer processor module, to be cooled.

This application is a continuation in part of application Ser. No.08/896,279 filed Jul. 16, 1997, now abandoned.

BACKGROUND OF THE INVENTION

The present invention is generally directed to providing reliablecooling systems for mainframe computer systems or for any electronicsystem requiring cooling. More particularly, the present invention isdirected to a redundant refrigeration system employing a single coldplate which preserves flow isolation between the fluids in the redundantsystems. In another aspect of the present invention, there is provided acombination of air and redundant refrigeration cooling for an electronicdevice such as a mainframe or server processing unit disposed within acabinet possibly along with other less thermally critical components. Inyet another aspect of the present invention, there is provided a modularrefrigeration unit capable of operating continuously in a variety ofambient conditions and under a variety of thermal loads.

In recent years, the semiconductor industry has taken advantage of thefact that CMOS circuits dissipate less power than bipolar circuits. Thishas permitted more dense packaging and correspondingly faster CMOScircuits. However, almost no matter how fast one wishes to run a givenelectronic circuit chip, there is always the possibility of running itfaster if the chip is cooled and thermal energy is removed from itduring its operation. This is particularly true of computer processorcircuit chips and even more particularly true of these chips whendisposed within multi-chip modules which generate significant amounts ofheat. Because there is a great demand to run these processor modules athigher speeds, the corresponding clock frequencies at which thesedevices must operate become higher. In this regard, it should be notedthat it is known that power generation rises as a function of the squareof the clock frequency. Accordingly, it is seen that the desire forfaster computers generates not only demand for computer systems but alsogenerates thermal demands in terms of energy which must be removed forfaster, safer and more reliable circuit operation. In this regard, it isto be particularly noted that, in the long run, thermal energy is thesingle biggest impediment to semiconductor operation integrity.

In addition to the demand for higher and higher processor speeds, thereis also a concomitant demand for reliable computer systems. This meansthat users are increasingly unwilling to accept down time as a fact oflife. This is particularly true in the mainframe and server realms.Reliability in air-cooled systems is relatively easily provided byemploying multiple air-moving devices (fans, blowers, etc.). Otherarrangements which incorporate a degree of redundancy employ multipleair-moving devices whose speeds can be ramped up in terms of their airdelivery capacity if it is detected that there is a failure or needwithin the system to do so. However, desired chip-operating power levelsare nonetheless now approaching the point where air cooling is not theideal solution for all parts of the system in all circumstances. Whileit is possible to operate fans and blowers at higher speeds, this is notalways desirable for acoustic reasons. Accordingly, the use of directcooling through the utilization of a refrigerant and a refrigerationsystem becomes more desirable, especially if faster chip speeds are thegoal.

However, it is difficult to build redundancy into systems employingrefrigerants. Such redundant systems naturally require the utilizationof at least two separate refrigeration systems. This means that at leasttwo motor-driven compressors are required. However, it is wellrecognized that the compressor, representing a major moving partapparatus, is also one which is prone to mechanical failure. The desirefor zero down time and minimum maintenance requirements also make theutilization of multiple compressors difficult. These compressors shouldbe designed, controlled and set up so that various failure modalities donot bring the entire computer system down nor risk damage to thecomponents within the system. Furthermore, one should also be concernedabout refrigerant leaks. Accordingly, the refrigerant systems forredundant cooling must be designed so that the refrigerant loops are notin flow communication with one another so that a leak in one loop wouldbring down the whole system. However, there are great practicaldifficulties in doing this since it requires two separate loops whichare maintained in flow-wise isolation from one another and yet, at thesame time, requires the utilization of refrigerant loops which are invery close thermal proximity with one another at the point within a coldplate which is attached (or otherwise thermally coupled) to theelectronic circuit module or system to be cooled.

While certain electronic components or modules produce relatively largeamounts of thermal energy, it is often the case that these modules areemployed in conjunction with other electronic circuit components whichalso require some degree of cooling but do not operate at temperaturesso high as to require direct cooling via a cold plate and/or refrigerantsystem. If modules of varying thermal energy output are employed in thesame system, it is therefore desirable that the cooling systems employedfor the lower thermal output modules be cooled in a manner which iscompatible with cooling systems employed for the higher temperaturemodules. To the extent that a degree of cooperation between thesesystems can be provided, the net result is a system which is even morereliable and dependable. Nonetheless, these dual cooling modalities mustbe accommodated within a single cabinet or frame.

Another very desirable feature of any system which is employed to coolelectronic devices and systems, particularly computer systems, is that aseparate chilled water source not be necessary. While in some situationswhere the requirements are such that the inconvenience of chilled waterplumbing is offset by the needs and/or desires for extremely rapidcomputation and computer throughput, nonetheless, less stringentrequirements for computational speed are nonetheless preferablyaddressed through the utilization of machines which are air cooled. Thiscooling methodology is desirable in that it permits the utilization ofstand-alone units. These self-contained units are, everything else beingequal, a generally preferred solution to providing data processingserver solutions.

There are yet other requirements that must be met when designing coolingunits for computer systems, especially those which operate continuouslyand which may in fact be present in a variety of different thermalenvironments. Since computer systems run continuously, so must theircooling systems unlike a normal household or similar refrigerator whichis operated under a so-called bang-bang control philosophy in which theunit is alternating either totally on or totally off. Furthermore, sincelarge computer systems experience, over the course of time, say hours,variations in user load and demand, the amount of heat which must beremoved also varies over time. Therefore, a cooling unit or coolingmodule for a computer system must be able not only to operatecontinuously but also be able to adjust its cooling capability inresponse to varying thermal loads. And furthermore, since it is intendedthat these modular cooling units be used in groups of two or more toassure redundancy and since not all of these units are always intendedto be operating at the same time, there will be times when the thermalload is very small. Therefore, problems associated with low speedmotor/compressor operation must be addressed along with problemsassociated with starting and/or stopping the cooling unit when, forexample, normal scheduled switching between modular refrigeration unitsoccurs.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, anapparatus for cooling electronic circuits comprises a special cold platewith dual coolant flow passages. These passages are isolated from oneanother in the sense that they are not in flow communication and yet,nonetheless, these coolant flow passages are still in intimate thermalcontact with one another within the cold plate. In conjunction with thiscold plate, first and second refrigeration systems are employed toprovide a desired degree of redundancy. Each of these refrigerationsystems includes a compressor, condenser and expansion device connectedin a closed refrigerant loop with one of the passages in thedual-passage cold plate. In preferred embodiments of the presentinvention, there is also provided a control mechanism for operating thefirst and second refrigeration systems in a time-alternating fashion.Additionally, in preferred embodiments, there is also provided amechanism for reducing the power produced by the electronic system whichis being cooled in the event of a failure in one of the refrigerationloops.

In another embodiment of the present invention, a redundantly cooledelectronic system comprises a cabinet which has an air intake and an airexhaust. A planar circuit board, together with an electronic moduledisposed on the planar circuit board, is contained within the cabinet.An air-moving mechanism is provided for moving air from the inletopening to the exhaust opening past the electronic module. Theelectronic module (processor) has a cold plate which is in thermalcontact with it. The cold plate is as described above and possessesfirst and second coolant passages which are in turn connected toredundant first and second refrigeration systems. It is noted that inthe description contained herein, the reference to a redundant coolingsystem is primarily directed to the notion that two separate andisolated refrigeration systems are supplied. However, in a lesserintended sense, the term "redundant" also applies to the notion that inthe event of a complete failure in both of the refrigeration systems, acertain amount of air cooling can and will take place as the computersystem or other cooled electronic system is being shutdown.

In yet another embodiment of the present invention, a modularrefrigeration unit (MRU) is provided for supplying cooled refrigerant toone side of a dual-loop evaporator/cold plate. The MRU is enabled forcontinuous operation under various loads and in various thermalenvironments through the inclusion of a direct current (dc) motortogether with the further inclusion of a hot gas bypass value (HGBV)which bypasses the condenser and thermal expansion valve when themotor/compressor unit is operating under low thermal load conditions orupon startup. The unit is packaged in a single module which is easilycoupled into an already running computer processing system via two quickdisconnect refrigerant lines, a power cable and a signal cable.

Accordingly, it is an object of the present invention to provide asystem and method for cooling computer and other electronic systems.

It is another object of the present invention to provide a coolingsystem which possesses redundancy for the purpose of providinguninterrupted use of electronic equipment.

It is also an object of the present invention to provide a coolingsystem for electronic equipment which essentially preserves itsstand-alone, air-cooled nature.

It is yet another object of the present invention to provide a coolingsystem for electronic components in which air and refrigerant coolingare combined in an integrated package.

It is a still further object of the present invention to provide acooling system for electronic assemblies, modules and cards.

It is also an object of the present invention to provide a mechanismwhich utilizes two refrigerant loops which are thermally coupled but yetwhich are flow-wise isolated from one another.

It is an object of the present invention to provide a cooling system forelectronic components which include fail-safe means for operation in theevent of a number of different failure modalities, including refrigerantleakage.

It is also an object of the present invention to provide a system andmethod for continued computer usage in the event of cooling systemproblems.

It is a still further object of the present invention to provide a coldplate for electronic component cooling which preserves refrigerant flowisolation while at the same time maintaining good thermal connectivityto a module to be cooled and also provides good thermal conduction andflow-wise isolation between dual refrigerant loops.

It is a still further object of the present invention to provide anelectronic component cooling system which is self contained.

It is also an object of the present invention to provide a computer orelectronic system in which the refrigerant cooling system is arack-mountable, field-replaceable unit.

It is also an object of the present invention to provide a coolingsystem for an electronic module which can be attached to a refrigerationsystem by means of flexible and detachable refrigerant supply lines.

It is yet another object of the present invention to provide arefrigeration unit which is capable of operating continuously.

It is still another object of the present invention to provide arefrigeration unit which is capable of variable heat removal capacity,particularly in response to varying thermal demands.

It is a still further object of the present invention to provide arefrigeration unit which is easily startable, easily shut down and iscapable of running under low thermal load situations.

It is also an object of the present invention to provide a refrigerationsystem which is capable of operating in a wide range of ambient andthermal load conditions.

Lastly, but not limited hereto, it is an object of the present inventionto provide a system and method for facilitating the operation ofcomputer systems at higher speeds and, in particularly, for doing so ina reliable manner so as to be able to maintain such systems incontinuous operation for as long a time as is reasonably possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the concluding portion of thespecification. The invention, however, both as to organization andmethod of practice, together with the further objects and advantagesthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings in which:

FIG. 1A is a side elevation view illustrating the arrangement ofcomponents in a preferred embodiment of the present invention;

FIG. 1B is a view similar to FIG. 1A but more particularly illustratinga front view;

FIG. 2 is a block diagram illustrating a dual redundant refrigerationsystem for utilization with a cold plate in accordance with the presentinvention;

FIG. 3 is a block diagram illustrating the control system for operationof the redundant system shown in FIG. 2;

FIG. 4 is a functional block diagram illustrating an arrangement for aredundant cooling system for multiple electronic modules;

FIG. 5 is a view similar to FIG. 4 illustrating an alternativearrangement for the situation where multiple modules must be cooled;

FIG. 6 is a functional block diagram illustrating an alternateredundancy arrangement for cold plate cooling;

FIG. 7 is a side elevation view similar to FIG. 1A but more particularlyillustrating an alternative air flow path;

FIG. 8A is a top view of a central cold plate portion which provides thedesired degree of thermal coupling and flow isolation desired in thepresent invention;

FIG. 8B is a side elevational cross-sectional view of the cold plateportion shown in FIG. 8A together with upper and lower sealing plates;

FIG. 9A is a view similar to FIG. 8A but more particularly illustratinga situation in which the flow paths are provided in more isolatedchannels on opposite sides of the central plate portion;

FIG. 9B is a cross-sectional view of the cold plate portion of FIG. 9Afurther including top and bottom sealing plates;

FIG. 10A is a top view of a cold plate center portion illustrating analternative parallel path arrangement for thermally coupled, yetflow-wise isolated channels;

FIG. 10B illustrates a cross-sectional view through the cold plate ofFIG. 10A;

FIG. 10C is a cross-sectional view similar to FIG. 10B more particularlyshowing the cross section through an end manifold portion;

FIG. 11A is a view similar to FIG. 10A but particularly illustrating anembodiment in which the flow channels in the top and bottom portions aredisposed adjacent to one another instead of being in alternatingpositions;

FIG. 11B illustrates a cross-sectional view through the cold plate ofFIG. 11A;

FIG. 12 is an isometric view illustrating the modular refrigeration unitof the present invention with covers removed to provide an internal viewof the configuration of its subcomponents and also particularlyillustrating anti-vibration tubing configuration; and

FIG. 13 is an isometric view similar to FIG. 12, but more particularlyillustrating a closed MRU together with its quick disconnect connectorsfor attachment to a cold plate and/or evaporator.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a side view of one embodiment of the presentinvention. This invention employs cabinet 10 having inlet opening 11 andoutlet opening 12 for the passage of air therethrough. The flow of airis induced by means of one or more blowers 15. Fans or other air-movingdevices could also be employed for this same purpose. However, blowersare preferred because of their efficiency. In the apparatus shown inFIG. 1A, air moves from inlet 11 in cabinet 10 to exhaust 12 along airflow line 13. The flow of air is employed for the particular purpose ofcooling certain of the electronic components disposed on printed circuitcards or so-called "books" 20. Air flows down between these books orcards through blower(s) 15 to plenum 16 and thence through cards 20' onthe other side of mother board 50 into which books 20 are inserted.Thus, having flowed passed cards 20 and 20', air stream 13 exits throughexhaust 12 in cabinet 10.

The description provided thus far is therefore seen to disclose theprimarily preferred method for cooling certain ones of the electroniccomponents, namely, those components located on cards 20 and 20' whichare of sufficiently low power that air cooling is an appropriatemodality. However, a major aspect of the present invention is directedto the specific means and systems employed for cooling electronic module151. In preferred embodiments of the present invention, module 151includes circuits for data processor components associated with amainframe or server computer system. In particular, the system shown inFIGS. 1A and 1B illustrates the placement of cold plate 150 which formsa significant aspect of one embodiment of the present invention. Coldplate 150 is connected by means of flexible refrigerant lines (not shownfor clarity) to a refrigeration system present in the upper portion ofcabinet 10 above shelf 131. The refrigeration system for cooling coldplate 150 and, thus, module 151 includes items such as motors,compressors and condensers together with an expansion device. Thus, thesystem shown in FIGS. 1A and 1B represents an apparatus in which bothair cooling and direct refrigerant cooling is employed. It isparticularly useful for a proper understanding to note that electronicchip module 151 is not mounted in a sideways fashion as are cards 20primarily because of the fact that module 151 typically possesses a verylarge number of pins for achieving connection and communication withother circuits in the computer and/or with other computer systems. Thus,the I/O (input/output) pin requirements for module 151 dictate that itpreferably be mounted in the fashion shown. In FIG. 1B, this electronicmodule is shown disposed beneath cold plate 150 which is visible in FIG.1B.

As shown in the figures, area 17 may include the same components asshown in the top half of the cabinet. Additionally, area 17 may alsoinclude power supply components (a power cage, e.g.) along with its ownair-moving device. However, the components disposed in area 17 are nototherwise relevant to the present invention.

In order to provide the desired degree of system cooling redundancy, adual refrigeration system, such as that shown in FIG. 2, is provided inaccordance with preferred embodiments of the present invention. Theheart of this dual refrigeration system is the inclusion of cold plate150 which has contained therein isolated coolant passages for a firstrefrigerant loop (circuit A) and a second refrigerant loop (circuit B).The cold plate itself may be constructed in several different ways. Thecold plate and its construction is more particularly described belowwith reference to FIGS. 8A, 8B, 9A, 9B, 10A, 10B and 10C. The primaryfeature of cold plate 150 is that the coolant passages contained thereinare isolated from one another in a flow-wise fashion. That is, coldplate 150 is designed so as to prevent leakage or seepage from onerefrigerant loop (circuit A) to the other refrigerant loop (circuit B).Nonetheless, in spite the flow-wise isolation, the two coolant loopsprovided are, nonetheless, in intimate thermal contact with one anotherand with the body of the cold plate so as to remove heat from module 151in an efficient manner.

Thus, in accordance with the redundancy requirements of the presentinvention, FIG. 2 illustrates a refrigerant system for circuit A and arefrigerant system for circuit B. In particular, motor 100 drivescompressor 101 which is connected to condenser 103 by means of supplyline 102. Likewise, condenser 103 is connected to circuit B for coldplate 150 by means of supply line 104 which passes through filter/dryer70 which functions to trap particulate matter present in the refrigerantstream and also to remove any water which might have become entrained inthe refrigerant flow. Subsequent to filter/dryer 70, refrigerant flowpasses through expansion device 105. Expansion device 105 is preferablyan expansion valve. However, it may also comprise a capillary tube orthermostatic valve. Thus, expanded and cooled refrigerant is supplied tocircuit B in cold plate 150. Subsequent to its picking up heat frommodule 151 through the body of cold plate 150, the refrigerant isreturned via return line 106 to accumulator 60 which operates to preventliquid from entering compressor 101. Accumulator 60 is also aided in itsfunction by the inclusion of smaller capacity accumulator 65 which isincluded in preferred embodiments of the present invention to provide anextra degree of protection against the entry of liquid phase refrigerantinto compressor 101. Subsequent to accumulator 65, vapor phaserefrigerant is returned to compressor 101 where the cycle repeats. Inaddition, circuit A is provided with hot gas bypass value (HGBV) 97which, as its name suggests, operates to pass hot refrigerant gassesfrom compressor 101 directly to cold plate 150. HGBV 97 is controllablein response to the temperature of cold plate 150 which is provided bymodule temperature sensor 185 which is preferably a thermistor deviceaffixed to cold plate 150 at any convenient location. In preferredembodiments, HGBV 97 (and other HGBVs discussed herein) areelectronically controlled. The HGBVs preferably employed herein arecontinuously throttleable but are currently operated in fully open andfully closed modes for convenience of design. The HGBVs operate to shunthot gasses directly to cold plate 150 when its temperature is alreadysufficiently low. In particular, under these low temperature conditions,motor 100 runs at a lower speed in response to the reduced thermal load.At these lower speeds and loads, there is the danger of motor 101stalling. Upon detection of such a condition, HGBV 97 is opened inresponse to a signal supplied to it from microprocessor control 195 (seeFIG. 3).

In an exactly analogous fashion, refrigerant flows in the loop incircuit A which includes compressor 111, line 112, condenser 113,filter/dryer 170, expansion device 115, cold plate 150, return line 116which connects to accumulator 160, which in turn connects (side A) tosmaller accumulator 165 and thence back to compressor 111 which isdriven by motor 110. As in circuit B, circuit A also includes HGBV 197,as shown.

The system shown in FIG. 2 lends itself to operation in severaldifferent modes. For example, it is possible to design each of the twoseparate refrigeration systems so that each one is capable of removingall of the desired heat generated by electronic module 151. If such isthe case, it is not necessary to run both refrigeration systems at thesame time. Nonetheless, because of the desirability of maintaining sealsin a wetted or moistened state, it is not desirable to shut off eitherone of the two refrigeration systems for extended periods of time. Thus,in the circumstance where either refrigeration system is capable ofproviding the desired cooling, it is desired to control these systems ina manner so that as one is being shut down, the other is being turned onand being brought up to speed so that the other system may "rest". Inpreferred methods of operation, the separate refrigeration systems areeach run for about 24 hours, at which time the other system is broughtonline and the first system is shortly thereafter shut down.

In those circumstances where the design of the refrigerant portions ofthe cooling system is such that both systems are required during normaloperation, one must consider the possibility of the proper course ofaction to follow in the event that one of the refrigeration systemsfails. Clearly, soft failure modalities are preferred. In order toeffectuate such control, certain instrumentation readings are preferablyprovided to microprocessor cooling system controller 195, as shown inFIG. 3. Controller 195 has, as its principal design object, control ofthe temperature of module 151 and/or cold plate 150. In particular,desirable inputs for the cooling system controller include speed sensor180 for motor A, speed sensor 190 for motor B, coolant temperaturesensor 181 for circuit A, coolant temperature sensor 191 for circuit Band module temperature sensor 185 for module 151 and/or cold plate 150.Temperature sensors 181 and 191 are placed at the compressor exhaust andare used primarily for diagnostic purposes. Based upon these signalinputs, cooling system controller 195 provides signals to motorcontroller 196 to turn on either or both of motors 100 and 110 in FIG.2. Additionally, cooling system controller 195 also preferably providesa "circuit power signal" which is provided as input to electronicprocessor module 151 as a signal that there is a cooling system problemand that the module should be operated at reduced power levels, say forexample, by causing a reduction in the clock speed. In this manner, asolution to the cooling system problem including refrigerant orrefrigeration system replacement may be effected while at the same timemaintaining computer center operations although at a reduced pace and ata concomitantly reduced thermal load. Furthermore, in normal modes ofoperation, microprocessor controller 195 also controls HGBVs 97 and 197,as discussed above. Microprocessor controller 195 may comprise aprocessor unit dedicated to control purposes or, in fact, the functionsof microprocessor 195 may be provided by programming code running withincomputer processor modules which are cooled by the refrigeration systemherein and more particularly by programming running within microcodedportions of such a computer processor.

The redundant cooling system, shown in FIG. 2, is also employable inthose situations where more than one electronic module is to be cooled.In these circumstances, each module is provided with its own cold plateand with its own expansion device. Accordingly, FIG. 4 illustrates thesituation in which both cold plates 150' and 150" are to be cooled. Inthe situation shown in FIG. 4, each of the cold plates possesses dualpassages which are thermally coupled but which are flow-wise isolated,that is, there is no flow communication between these passages.

Redundant cooling with flow isolation and refrigerant separation ismaintained in the system shown in FIG. 4 by providing a supply line fromcondenser 103 to side B of cold plate 150' through line 104,filter/dryer 70, expansion device 105 and line 104'; similarly, supplyline 104" supplies the circuit for side B of cold plate 150" fromexpansion device 115. Circuit B in both cases is completed by means ofreturn lines 106' and 106" which return refrigerant from 150' and 150",respectively, either directly to compressor 101 or to common return line106. (Accumulators 60 and 65, shown in FIG. 2, are also shown in FIG.4.) Hot gas bypass valves 97 and 97' serve the same function asdescribed above, only now HGBV 97 and HGBV 97' are controlled as afunction of the temperature of cold plate 150' and HGBV 197' and HGBV197 are controlled as a function of the temperature of cold plate 150".An exactly analogous system is provided for circuit loop A in cold plate150" through the supply and return lines shown which include compressor111, condenser 113, filter/dryer 170, HGBVs 197 and 197' andaccumulators (160 and 165), and expansion devices 105' and 115' in arefrigerant loop.

FIG. 5 illustrates in simplified form another approach to the problem ofcooling multiple modules 150' and 150". (For simplicity and ease ofunderstanding, filter/dryers, accumulators and HGBVs are not shown sincetheir placement and use is already clear from FIGS. 2 and 4.) In theembodiment shown in FIG. 5, the arrangement shown in FIG. 2 isessentially replicated for new cold plate 150". In the embodiment shownin FIG. 5, there are accordingly four separate cooling loops, namely,circuits A and B associated with compressors 101A and 101B,respectively. Likewise, coolant loops for sides C and D of evaporator150" are associated with compressors 101C and 101D together with theirappropriately and correspondingly labeled associated elements such assupply and coolant lines, expansion devices, condensers and motors. Themulti-chip cooling solution illustrated in FIG. 5 is one possiblealternative; however, it is not a preferred alternative in that itdoubles the number of components (motors, compressors, condensers,accumulators, filter/dryers, HGBVs, etc.) that are required.

Yet another embodiment which provides redundancy in a refrigerationcooling system for cold plate 150 is shown in FIG. 6. In thisembodiment, redundancy is provided only insofar as the motors (100a and100b) and the compressors (101a and 100b) are concerned. FIG. 6 has theadvantage in that cold plate redesign is not required. In such anembodiment, cold plate 150 includes only a single coolant flow passage.

Nonetheless, the embodiment shown in FIG. 6 does provide a degree ofredundancy by providing two motors and two compressors for compressingthe refrigerant which is supplied to them via return line 106 fromsmaller accumulator 65 which is connected in the compressor return lineto larger accumulator 60. The embodiment shown in FIG. 6 does not,however, provide redundancy protection, in the event that there is aproblem (for example, a leak) in supply line 102, in condenser 103, insupply line 104, in expansion device 105, in cold plate 150 or in returnline 106. Accordingly, the degree of redundancy protection provided bythis embodiment is limited. Nonetheless, there is redundancy in that theelectronic module cooled by cold plate 150 may still receive coolantfrom an operative one of the motor/compressor combinations. In such acircumstance, upon failure detection in one of the motor/compressorcombinations, the other motor/compressor needs to be isolated fromoperating part of the system. Accordingly, for this purpose, shutoffvalves 141 and 142 are actuated simultaneously to isolate compressor101a. In a similar fashion, shutoff valves 143 and 144 serve to isolatecompressor 101b. This embodiment also employs HGBV 97 which functions asdescribed above.

Another embodiment of the present invention is illustrated in FIG. 7.FIG. 7 is similar to FIGS. 1A and 1B but it more particularlyillustrates the fact that a different air circulation flow path 13' maybe provided which also acts to remove heat from condensers 103 and/or113. This mechanism is provided by opening 132 in shelf 131 (in cabinet10) which supports the refrigeration components. Correspondingly,exhaust opening 12 is moved upward to position 12', as shown in FIG. 7.Since it is primarily desirable that the condensers be cooled as opposedto the motor-compressor combinations which may or may not requirecooling, barrier 130 is provided to ensure that air flow path 13' isdirected across condensers 103 and 113 through exhaust opening 12'.

Attention is next directed to the design of cold plate 150 (or 150' or150" as appropriate). The embodiments shown in FIGS. 8A, 8B, 9A, 9B,10A, 10B, 10C, 11A and 11B are particularly directed to those situationsin which redundancy is provided in a manner which includes two entirelyseparate and distinct cooling circuits (referred to above as circuits Aand B). These figures also include section lines B and C since, in eachcase, cross-sectional views are provided for a better understanding ofthe structure of the cold plate. In all of the cold plate embodimentsillustrated in FIGS. 8-11, separate but thermally coupled flow passagesare provided. In preferred embodiments of the present invention, coldplates illustrated in FIGS. 8-11 preferably comprise a material such asaluminum or copper. However, any highly thermally conductive materialmay be employed. However, it is desirable that the material berelatively easily machinable. Also, because it would be clearlydifficult to provide a serpentine channel embedded in a monolithic pieceof material, each of the cold plate constructions illustrated in FIGS.8-11 employ a central path defining structure (200, 300, 400, 500)together with top plates (210, 310, 410, 510) and bottom plates (220,320, 420, 520), respectively.

In one embodiment of a desirable cold plate such as that illustrated inFIGS. 8A and 8B, serpentine but isolated passages 205 and 206 areprovided so that they co-exist at the same depth within central block200. For purposes of cooling uniformity, both sets of passages 205 and206 are arranged in a symmetric, serpentine, interdigitated fashion,such as that shown. Furthermore, passage 205 is provided with inletopening 201 and exit opening 203. In a similar fashion, passage 206 isprovided with outlet opening 202 and inlet opening 204. In this regard,it is particularly noted that, in preferred embodiments of the presentinvention, the dual passage cold plate is connected into therefrigeration system so that the inlet for circuit A is adjacent to theoutlet for circuit B in the cold plate itself. In those circumstanceswhere both circuits are being operated at the same time, thisarrangement provides a more uniform cooling of the electronic module.This same preference also applies to the cold plate embodimentillustrated in FIGS. 9A and 9B.

In particular, the cold plate design shown in FIGS. 9A and 9B is suchthat separate cooling passages 305 and 306 are provided in much the sameway as shown in FIGS. 8A and 8B except that passage 306 lies at thebottom of the cold plate while passage 305 is disposed at the top (asseen in FIG. 9A). This is more particularly illustrated in thecross-sectional view shown in FIG. 9B. In the same manner as discussedabove, passage 305 includes inlet opening 301 and exit opening 303 forconnection to coolant circuit A or B. In a similar manner, passage 306is provided with exit opening 302 and entrance opening 304. Naturally,the role of exit and entrance openings can be reversed in the cold platedesign shown in any of FIGS. 8A-10C.

Another embodiment for a dual passage cold plate is shown in FIGS.10A-10C. In this particular embodiment, instead of providing serpentine,interdigitated passages, passages 405 and 406 are straight but stillmaintain their interdigitated geometry. Instead of having a serpentinegeometry, each set of passages is instead served by an entrance and exitmanifold. For example, upper passages 405 in FIG. 10A are served bymanifold 407 which is in flow communication with coolant connectionopening 402. Cooling fluid flows in through opening 402 to manifold 407through passages 405 to exit manifold 408 and alternately to exitopening 404. A corresponding function is provided via entrance opening403 which serves a manifold which supplies passages 406 which emptiesinto an exhaust manifold which in turn supplies heated coolant fluid toexit opening 401 which services the lower set of cooling passages.

A fourth embodiment of a dual passage cold plate is shown in FIGS. 11Aand 11B. In this embodiment, a multiplicity of straight passages 505 and506 are provided on each side of central block 500. Upper passages 505in FIG. 11A are served by manifold 507 which is in flow communicationwith coolant connection opening 501. Cooling fluid flows in throughopening 501 to entrance manifold 507 through passages 505 to exitmanifold 508 and through outlet opening 503. A corresponding function isprovided for the lower set of passages via entrance opening 502 whichsupplies passages 506 emptying into an exhaust manifold allowing heatedcoolant to leave via exit opening 504. It should be understood that, inthis arrangement, heat entering the cold plate structure across bottomplate 520 has a greater distance to travel to reach upper passages 505and thereby exhibits a greater thermal resistance than for bottompassages 506, all other things being equal. It should be appreciated,however, that an increased number of cooling passages may be placed inthe cold plate in this configuration and that, additionally, anincreased number of passages 505 may be used on the top than on thebottom so as to offset the longer heat flow path and provide the sameoverall thermal resistance whether coolant flows through upper passages505 or lower passages 506.

The upper and lower plates for the cold plates illustrated in FIGS. 8-11are affixed to central blocks 200, 300, 400, 500 in any convenientfashion. For example, they can be attached by brazing, soldering or evenby gluing. However, in the case of attachment via epoxy, it is desiredthat the thermal resistance created by the attachment, particularly forthe lower cover, is within an acceptable range. As indicated above, itis one of the primary objectives of the cold plate design employedherein to preserve flow-wise isolation between the coolant flow in thetwo sets of passages. It should be particularly noted that theembodiments illustrated in FIG. 9A, 9B, 10A, 10B, 10C, 11A and 11B areparticularly advantageous in this regard. These embodiments completelyeliminate the possibility of fluid leaking between the two circuitswithin the cold plate.

In preferred embodiments of the present invention, it is clearlydesirable that the cold plate be made as flat as possible to conform tothe exterior packaging of electronic module 151. However, in thosecircumstances in which module 151 comprises a curved or even a steppeddesign, it is nonetheless possible to provide an appropriate cold plateby correspondingly machining or molding one of the upper or lower plates(covers) shown in FIGS. 8-11. However, in general, a good flat thermalmating surface is preferable.

FIG. 12 is an isometric view illustrating a preferred configuration forone side of the modular refrigeration system illustrated in FIG. 2. Inparticular, it is seen that cabinet or housing 600 contains condenser103 which is of substantially standard design except that it preferablyincludes S-shaped aluminum fins which create an improved flow of coolingair through condenser 103. Furthermore, condenser 103 preferablyincludes tubing having rifled internal ridges to improve its efficiency.These are fine internal ridges which help to promote heat transfer.Likewise, FIG. 12 illustrates the presence of motor/compressor unit100,101, hot gas bypass valve 97 and two portions, bulb 105' and coiledloop 105", of the thermal expansion device. Large accumulator 60,together with smaller accumulator 65, are also shown. It is alsoimportant to note the presence of loops 900 and 901 in coolant conduits.These loops have been seen to be very desirable additions to thestructure in that they help to eliminate vibration in the system.Vibration could otherwise be a problem particularly at low motor speeds.

It is also noted that cabinet or housing 600 includes four-pin socket601 for supplying power to motor/compressor 100,101 and bracket 603 forsupporting a printed circuit board containing control circuitry. Signalsto and from this board may be supplied via multi-pin DIN socket 602.Connection to evaporator/cold plate 150 is provided through quickdisconnect couplers 604 and 605. FIG. 13 more particularly shows theclosed cabinet together with quick disconnect conduits 606 and 607 whichare attached to quick disconnect sockets 604 and 605, respectively, as ameans for supplying cooled refrigerant to evaporator/cold plate 150.

From the above, it should be appreciated that the systems and apparatusdescribed herein provide a reliable redundant cooling system forcomputer and other electronic systems. It should also be appreciatedthat the cooling systems of the present invention permit the operationof computer systems at increased speeds. It should also be appreciatedthat the objects described above have been filled by the systems andmethods shown herein particularly with respect to the utilization of acold plate having dual flow-wise isolated but thermally coupledpassages.

While the invention has been described in detail herein in accordancewith certain preferred embodiments thereof, many modifications andchanges therein may be effected by those skilled in the art.Accordingly, it is intended by the appended claims to cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

The invention claimed is:
 1. A cold plate having flow-wise isolated dualpassages, said cold plate comprising:a central plate having a first saidcentral plate channel extending only partially through from a first sideof said central plate and disposed in a serpentine pattern andpossessing an inlet opening at one end of said first channel and anoutlet opening at the other end of said first channel, said centralplate also possessing a second channel extending only partially throughsaid central plate from a second side of said central plate and alsodisposed in a serpentine pattern and also possessing an inlet opening atone end of said second channel and possessing an outlet opening at theother end of said second channel, said first and second channels beingdisposed, with respect to each other, in an interdigitated fashion; atop plate sealably affixed to a said first side of said central plate,said top plate having openings therein to provide access to said inletand outlet openings for both said first and second channels; and abottom plate sealably affixed to the second side of said central plate,whereby two separate, but flow-wise isolated passages are formed.
 2. Acold plate having isolated dual passages, said cold plate comprising:abase plate having a first channel extending only partially into a topside of said base plate and being disposed in a serpentine pattern andpossessing an inlet opening and an outlet opening, said base plate alsopossessing a second channel extending only partially into said top sideof said base plate and also being disposed in a serpentine pattern andalso possessing an inlet opening and an outlet opening, said first andsecond channels being disposed, with respect to each other, in aninterdigitated fashion; and a top plate sealably affixed to said topside of said base plate, said top plate having openings to provideaccess to said inlet and said outlet openings for both said first andsecond channels.